1. Technical Field
The presently disclosed subject matter relates to a light source device which uses a plurality of LED devices or the like as a light source. The presently disclosed subject matter also relates to a vehicle lighting device utilizing the light source device, such as a headlight, an auxiliary headlight, tail-light, fog light, signal light, or the like.
2. Related Art
A conventional light source device utilizing an LED device has been known for use in a vehicle headlight, an LED lamp for use as a light source, and the like.
An example of a conventional vehicle headlight is disclosed in Japanese Translation of PCT Application No. 2003-503815 (corresponding to PCT Publication No. WO 01/001037) as shown in FIG. 1. The vehicle headlight of this type includes a light source which is composed of a plurality of light emitting diodes 1 arranged side by side, and an optical member (not shown) such as a lens located in front of the light source.
In this configuration, the light emitted from the respective light emitting diodes 1 passes through the optical member, such as a lens, located in front of the light source. The light, to which a light distribution property has been imparted by the optical member, is then externally emitted. This can provide a desired light distribution property for the vehicle headlight.
FIG. 2A shows another lighting device including an LED lamp as disclosed in Japanese Patent Application Laid-Open No. 2006-048934 (corresponding to U.S. Patent Publication No. 2006/022211A1). The lighting device utilizes an LED lamp 2 composed of a plurality of LEDs 2b (refer to FIG. 2B) and a concave reflector 3 having a focus near the light emitting area of the LED lamp 2. The plurality of LEDs 2b are arranged on the substrate 2a so as to provide an illumination pattern similar to that of a filament type light source.
By this structure, the light emitted from the LED lamp 2 is reflected by the reflector 3 and projected toward the illumination direction (forward direction). Accordingly, the image of the light emitting portion of the LED lamp 2 is projected forward to provide desired light distribution characteristics.
FIG. 3 shows another type of headlight disclosed in Japanese Patent Application Laid-Open No. 2001-076510. In contrast to the headlight and the lighting device described above utilizing LED devices, this headlight is configured to be a typical projector type headlight 4, which is composed of a bulb 5 as a light source, a reflector 6, a projection lens 7, and a light-shielding member 8.
The reflector 6 is composed of an elliptic reflecting surface having a first focus (a rear-side focus) near the bulb 5 and a major axis extending horizontally toward the front illumination direction, and an inner surface that serves as a reflecting surface.
The projection lens 7 is composed of a convex lens or an aspherical lens having a rear-side focus, and is disposed so that the rear-side focus is located near the second focus of the reflector 6.
The light-shielding member 8 is arranged near the second focus of the reflector 6 so as to provide the light projected toward the front illumination direction with a desired low-beam light distribution pattern. The light-shielding member 8 has an upper edge 8a with a predetermined shape in order to form a cut-off line in the light distribution pattern.
Light emitted from the bulb 5 of the headlight 4 configured as described above is directly incident on the projection lens 7 to be projected in the front illumination direction. Alternatively, the light is reflected by the reflector 6 to be focused near the second focus of the reflector 6 and the virtual image formed near the focus is reversed by the projection lens 7 to be projected in the front illumination direction.
Part of the virtual image is shielded by the light shielding member 8 so that the cut-off line C is formed by the upper edge 8a of the light shielding member 8 (see FIG. 4). The shaped virtual image is projected forward as a low beam.
FIG. 4 shows the virtual image, and this image is horizontally and vertically reversed by the projection lens. This can provide a light distribution pattern for right-side traffic. The pattern is designed not to include part of a left side area from the center of the luminance distribution by the cut-off line C in order to prevent any glare of light towards an opposite traveling vehicle.
As described above, typical vehicle headlights should provide light distribution patterns including a low-beam pattern (passing-by pattern), a high-beam pattern (traveling pattern), and the like. In the description, the light distribution pattern having a cut-off-line C is defined as a cut-off pattern.
The vehicle headlight disclosed in Japanese Translation of PCT application No. 2003-503815 (corresponding to PCT publication No. WO 01/001037) includes a plurality of light emitting diodes 1 arranged side by side in order to provide a desired or required light intensity—enough for a lighting device.
However, a desired light distribution pattern may not be obtained only by the light source in which the light emitting diodes are arranged side by side. In order to provide a desired light distribution pattern, the vehicle headlight can have an optical member for controlling the light distribution pattern arranged in front of the light source.
Further, this vehicle headlight is configured to improve the visibility around the vehicle. Accordingly, the vehicle headlight disclosed in this PCT publication is not designed for the purpose of ensuring the driver's field of view by projecting light in the front illumination direction.
The lighting device including an LED lamp disclosed in Japanese Patent Application Laid-Open No. 2006-048934 uses a single package incorporating a plurality of LED chips in order to obtain a desired or required light intensity—enough for a lighting device.
In this LED lamp including a plurality of LED chips, the light emitting portion is formed in a shape similar to the shape of a filament and utilizes a particular reflecting surface used in a conventional projector type headlight, thereby obtaining a desired light distribution pattern.
In doing so, the particular reflector located in back of the light source, and in some cases a light shielding member located in front of the light source, should be provided in order to obtain a desired light distribution pattern.
In this instance, however, it is difficult to obtain a desired or required light distribution pattern using only a single LED lamp. In order to cope with this problem, the headlight adopts a double-lamp system utilizing a plurality of LED lamps. In this case, however, the entire size of the lighting device is enlarged. Furthermore, since the headlight should have a reflector, the entire weight of the lighting device is increased. This weight increase is not preferable for achieving the Adaptive Front-Lighting System (AFS) which is recently popular. This is because a large load is unfavorably applied to the drive mechanism in an AFS device.
Furthermore, since a plurality of LED chips are arranged within the lamp housing of the LED lamp, individual light emitting points of the LED chips can be recognized under some conditions. As a result, the luminance distribution of the headlight may finely vary, whereby an appearance of the headlight may deteriorate.
The headlight disclosed in Japanese Patent Application Laid-Open No. 2001-076510 also calls for a reflector, and in some cases, a light-shielding member inside the lighting device. Accordingly, the entire weight and size of the lighting device is increased and the depth thereof may be approximately 130 mm.
Furthermore, the reflector for use in this headlight should be designed so as to correspond to the shape of the light emitting portion of the bulb serving as a light source. The planning and designing of such a reflector may take relatively longer time.